Moderna Launches Landmark Bird Flu mRNA Vaccine Trial in UK and US
Moderna has begun the world's first late-stage human trial of an mRNA-based bird flu vaccine, with 3,000 participants being recruited across 26 sites in England and Scotland as scientists race to prepare for a potential pandemic.
The Phase 3 clinical trial of Moderna's mRNA-1018 vaccine candidate began on 21 April 2026, marking the first time an mRNA technology-based pandemic bird flu vaccine has advanced to late-stage human testing. The trial, which is supported by a $54.3 million investment from the Coalition for Epidemic Preparedness Innovations (CEPI), aims to enrol approximately 4,000 healthy adults aged 18 and older across the US and UK.
UK Participation
In the UK, 3,000 patients will participate across 26 sites in England and Scotland, with half of these participants being over 65 — a group considered at higher risk from severe influenza. Researchers are also actively recruiting individuals with close contact with poultry, such as farmers, due to their higher risk of exposure to the H5N1 virus. The trial is backed by the National Institute for Health and Care Research (NIHR) in the UK.
The trial is expected to run for seven months, with participants receiving two doses of the vaccine or a placebo, three weeks apart. Early trials of mRNA-1018 indicated it was "generally well tolerated," with mostly mild to moderate side effects and no safety concerns, and showed a strong immune response as early as seven days after the first injection.
Why It Matters
Experts emphasise that while human-to-human transmission of the A(H5N1) strain is not yet common, the virus is "evolving and spreading" rapidly among animals, making human-to-human transmission a "real possibility." Since 2024, there have been 116 confirmed human cases worldwide, almost all linked to close contact with infected animals.
Dr Richard Pebody, director of epidemic and emerging infections at the UK Health Security Agency (UKHSA), highlighted that a flu pandemic is the most likely future pandemic, and this trial is a critical step in strengthening national readiness. For more, see BBC News' report.
What's Next?
Under its agreement with CEPI, Moderna has committed that if the vaccine receives regulatory approval and a flu pandemic is declared, it will allocate 20% of its mRNA-1018 manufacturing capacity for affordable supply to low- and middle-income countries. Results from the Phase 3 trial are expected within the next year, and could pave the way for regulatory approval and stockpiling of the vaccine as a pandemic preparedness measure.
